The present invention involves a control system for handling incoming direct inward dialed telephone calls (hereafter referred to as "DID").
Direct inward dialing was brought about to allow a caller to bypass the bottleneck of the switchboard and call directly to a person's desk or to an area of interest in a company office or plant.
These numbers were very inexpensive compared to the ordinary number that was rented from the telephone company, and it was common to order 100 numbers at a time. But even though 100 numbers were ordered, usually just a few pairs of wires (access lines) came in from the phone company to serve the 100 numbers.
Call forwarding came into vogue and allowed a person's telephone to be call forwarded to another number. The answering service providing such service, having several clients, didn't know whose number was being forwarded until the telephone company allowed another usage for DID numbers.
Now answering services assign individual DID numbers to each client who call forwards his line to the answering service. So the answering service has the identity of whose line is being called and may answer in the client's name. With such a system, a block of telephone numbers, e.g. 100 numbers, are assigned to a particular answering service and each block of telephone numbers is coupled to the answering service through access lines. These access lines, for example, can be coupled into the telephone system at the telephone central office at a location of the third from the last digit of the switching mechanism. For example, if a telephone number being called is 765-4321 then at the location of the output of the switch for the fourth digit (4) and before the switch for the fifth digit (3), an access line is coupled to the output of the fourth digit switch and all of the incoming calls bearing numbers 765-4--- are then sent along one of the access lines to the telephone answering system.
Over the past several years, complex multiterminal call forwarding devices have been developed. These devices serve to couple a telephone answering system to a plurality of access lines assigned to blocks of DID numbers of a telephone central office. Each system which is coupled to a plurality of access lines is controlled by one central computer control section. Such equipment has been developed as the primary member of a telephone answering system adapted to essentially stand alone without being used in conjunction with any other type of equipment except the individual telephones of the operators.
The telephone answering systems that have been developed have a plurality of incoming access lines coupling the system to several blocks of DID numbers. Such DID numbers typically have been used in conjunction with call forwarding devices. A particular subscriber with an individual telephone number sets up the subscriber's phone for call forwarding, and when the call comes to the subscriber it is then transferred to a number provided the subscriber by the telephone answering service. The call forwarding number provided to the subscriber is one of the numbers in the block of DID numbers that are rented by the telephone answering service. Each subscriber can be provided with a separate DID number of the block of numbers so that identification of the particular incoming DID number will fully identify the subscriber receiving the call.
While such systems have been extensively developed, the systems have been designed to be operated as totally independent members separate from any telephone switchboard. In addition, the systems have been designed to typically handle four or more access lines, and normally 5 to 10 access lines, coupling the system to the telephone central office. While there are four different access lines used in conjunction with the system, only a single computer has been used for controlling all of the handling of the incoming calls and distribution of the calls to various operators at the telephone answering service. With such an operation, if the computer of the system breaks down or malfunctions, then the entire system is down and the telephone answering service is completely out of commission.